Devices for pipe end alignment for joining together have been described in US2013/0145590. The focus of the device is to get axial alignment to facilitate threading or welding tubulars together for the purpose of extending a string to a subterranean location.
The application of magnetically impelled arc butt (MIAB) welding in forming strings to extend to a subterranean location is generally described in US2013/0092670. What is not addressed in this reference is the control of arc position particularly in thick walled tubulars. The tendency of the arc to wander between the inner and the outer wall of the tubulars to be joined was the subject of an analysis in T Sato, J Katayama, S Ioka & M Otani (1991); An Experimental Study of Rotational Behaviour of the Arc During Magnetically Impelled Arc Butt Welding; Welding International, 5:1, 5-10, DOI: 10.1080/09507119109447814. The article can also be found at: http://dx.doi.org/10.1080/09507119109447814. The article discusses the tendency of the arc to wander from an inside wall on initial heating to the outside wall as the heat builds and the arc circumferential speed picks up. The research examines the effects of arc strength and magnetic field strength on the migration of the arc as the heating process begins until the needed temperatures are achieved. With larger and thicker walled tubulars to be joined the issue of even heating becomes more important for achieving proper weld quality when the two tubular ends are pushed together to complete the joint. Too much localized heating can burn through small areas and preclude a quality joint. Some of these problems with arc management were discussed in the above article.
The present invention takes a different approach than the past MIAB welding research and techniques discussed above. The objective of arc management now centers on tubular position control as the prime controlled variable for desired arc tracking with respect to the wall of tubulars large and small and made of a variety of metals so as to optimize the weld quality when ends are joined together for completion of the welded connection. The arc location can be, for example, held at a steady location orbit approximately equidistant between the internal and external wall dimensions or alternatively, particularly for the larger diameters and thicker walled pipes the arc can follow an orbital and oscillating path with the goal of uniform heating of the entire wall end area where the two tubulars will make contact when pushed together. The control of the arc path is achieved by relative movement of the two tubular ends as the arc is induced to make circular or elliptical movement by the applied magnetic field. The movement can involve movement of one or both tubulars at the same time and all degrees of freedom for movement of the tubular ends is envisioned. For example, there can be relative rotational movement about a fixed longitudinal axis or relative axial movement about fixed and aligned longitudinal axes. The relative rotational movement of the tubulars rotating in tandem in opposite direction of the arc rotational direction compensates arc rotation speed limitation for tubulars with increased diameter and/or arc current direction dependent uneven heat up effects on tubular surface ends. Different turning directions and turning frequencies are used to heat up the ends of the tubulars differently or equally e.g. to connect tubular of different materials (e.g. different thermal conductivity, magnetic saturation, melting point) or wall thicknesses. Alternatively, there can be relative skewing between the longitudinal axes or relative lateral movement of the longitudinal axes without skewing them. The above mentioned movements and others can be combined. Cameras or other sensors can be used to track the arc location and movements to tie into the positioning system that will move one or both tubulars and keep or redirect the arc to the desired movement pattern with respect to the end wall areas of the opposed tubulars. Permanent magnets or solenoids further comprising an additional oscillating of the arc on its circular or elliptic path. Tubulars of any shape: round, elliptical or folded, might be connectable more precisely utilizing these technologies in combination. These and other aspects of the present invention will be more readily appreciated from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.